1. Field of the Invention
The invention relates to a device for measuring the thickness of a layer or coating on a ferrous and/or nonferrous substrate comprising a first measuring probe for a metal substrate containing iron, a second measuring probe for a metal substrate not containing any iron, evaluating electronics and a housing.
2. Description of the Prior Art
In various industrial branches metals, for example steel sheets, are provided with coatings or layers, for example paint layers or additional metal layers, to protect the metal substrate from outer influences.
In particular, in the automobile industry steel sheets are processed onto which one or more paint layers have been applied. The thickness of the paint layers can be detected when required using a magnetic inductive measuring method.
Meanwhile, however, the automobile industry also processes nonferrous metals in combination with steel sheets. Accordingly, such materials are also coated. In the automobile industry for example moving parts of the bodywork, such as doors, trunk lid and engine hood, are made from light alloy or nonferrous metal whilst the loadbearing parts are made from steel sheet.
To measure the layer thicknesses of the coatings applied to said parts, for example paints or lacquers, the manufacturers, the paint shops, customers or assessors must use two different measuring devices, the measuring device for the nonferrous metals or light alloys being based on the eddy current principle whilst the measuring device for the steel sheets is based on said magnetic inductive measuring method. Working with two different devices is complicated and costly.
Combination measuring devices provided a remedy to a certain extent but they also have a great number of disadvantages.
A known combination measuring device consists of two devices and it is necessary to connect measuring probes operating by the two measuring principles referred to above with respective cables to evaluation electronics disposed in a housing. The devices have to be switched over and prepared for the particular use by complicated calibrating steps. The costs and practical handling of this known device are therefore likewise disadvantageous. Moreover, frequently confusion between the particular measuring probes necessary occurs and consequently erroneous measurements and erroneous coatings cannot be avoided.
Another known measuring device comprises a combination probe which is to measure firstly by the magnetic inductive method and secondly by the eddy current method. This combination probe is however not able to adequately satisfy the two necessary measuring methods. For the combination probe constructed to be extremely compact is disadvantageous in so far as the combination part intended for the magnetoinductive measurement influences the combination part intended for the eddy current method and consequently the measuring error increases considerably. Due to these erroneous measurements a corresponding measuring device was taken off the market again shortly after its introduction.